Affinity chromatography in addition to ammonium sulfate, gel filtration, ion exchange chromatography and polyacrylamide gel electrophoresis will be utilized to purify rabbit serum atropinesterase and cocainesterase. Substrate specificity and kinetics data will be sought using purified enzymes. Aggregation and dissociation of multiple forms of human serum butyryl choline esterase (tropacocainesterase) will be studied. Separation of the active subunits in sufficient quantities for their individual characterization will be attempted.